1. Field of the Invention
This invention relates to sense amplifiers for use in memory circuits and more specifically, in static random access memory (SRAM) circuits.
2. Brief Description of the Prior Art
In memory circuits, especially those wherein the sense amplifier has a cross coupled circuit connection between the bit and bit lines, the sense amplifier is always connected to the bit lines. In SRAM primarily, it is necessary to disconnect the sense amplifier from the bit line during sensing the difference between a one and a zero on the bit line for performance reasons. This sensing generally takes place after the precharge portion of a clock cycle which has a precharge portion and a data sensing portion.
In the prior art, this problem has been resolved by using a switching device, e.g. a transistor, in the cross coupling circuitry to isolate the sense amplifier from the bit line, the switching device receiving a signal after precharge and before sensing to turn off the switching device and provide the required isolation. This procedure requires the existence of a transistor and control circuitry therefor. In addition, a time interval is required from the end of precharge to the commencement of bit line sensing to insure that the switch has been opened or turned off prior to a high speed seitching action in the sense amplifier, this causing a slowdown in the operation of the memory circuit. Still further, timing becomes critical to insure that sensing does not take place too soon or too late in respect to the switch transistor turn off. It is apparent that circuitry which could eliminate the need for such a switch could diminish the amount of circuitry required as well as provide an increase in speed or circuit response. Also, circuitry which would minimize the criticality of precise timing would also result in a diminution of erroneous results.